1. Field of the Invention
The present invention relates to a zoom lens and an image sensing apparatus, and for example, to a zoom lens which is used in an optical unit or the like for taking a video of a subject with an image sensor and which includes a zoom area with a relatively wide angle at a magnification variation ratio of 7× or larger, and also to an image sensing apparatus provided therewith.
2. Description of Related Art
In recent years, digital cameras have been in rapid spread, and have been not only used as means for simply downloading an image to a computer but also widely used as a tool, like a conventional silver salt camera, for leaving a photo. Accordingly, there have arisen increasingly strong demands for capabilities useful for leaving a photo (for example, high magnification variation ratio, wider angle, etc.) and also for compactification. In addition, due to trends toward a yearly increase in the number of pixels of an image sensor, there have arisen demands for achieving even higher optical performance. Also in devices (for example, a camcoder) for mainly downloading moving images, due to support of a still image photographing capability and hi-vision, etc., there have arisen demands for higher optical performance than in a conventional one.
As one of ways to meet these demands, Patent documents 1 and 3 suggest a zoom lens which arranges, in order from an object side, a first lens group having a positive optical power, a second lens group having a negative optical power, a third lens group having a positive optical power, a fourth lens group having a positive optical power, and a fifth lens group having a positive optical power, and which achieves a high magnification variation ratio. Moreover, Patents Documents 2 and 3 suggest a zoom lens which arranges, in order from an object side, a first lens group having a positive optical power, a second lens group having a negative optical power, a third lens group having a positive optical power, a fourth lens group having a negative optical power, and a fifth lens group having a positive optical power, and which achieves a high magnification variation ratio.                Patent Document 1: US2006/0056055A1        Patent Document 2: U.S. Pat. No. 7,177,092B2        Patent Document 3: U.S. Pat. No. 7,139,131B2        
The zoom lenses disclosed in Patent Documents 1 and 2 include in a zoom area a wide angle of view with a whole angle of view of 77 degrees and achieve a high magnification variation ratio of approximately 10×, but face a problem of a relatively large optical system size. In addition, in order to correct off-axis aberration associated with a wide angle of view, an aspherical surface molded with glass is used in a plurality of lens groups including the second lens group having a relatively large aperture, which brings about concerns about resulting cost increase. The zoom lens disclosed in Patent Document 3 has a relatively small optical system size but fails to simultaneously achieve a wide angle of view with a whole angle of view of over 70 degrees and a high magnification variation ratio of over 10×.